This paper presents a new algorithm to solve the problem of co-saliency detection, i.e., to find the common salient objects that are present in both of a pair of input images. Unlike most previous approaches, which require correspondence matching, we seek to solve the problem of co-saliency detection under a preattentive scheme. Our algorithm does not need to perform the correspondence matching between the two input images, and is able to achieve co-saliency detection before the focused attention occurs. The joint information provided by the image pair enables our algorithm to inhibit the responses of other salient objects that appear in just one of the images. Through experiments we show that our algorithm is effective in localizing the co-salient objects inside input image pairs.